I completed silent monastery 3 times and defeated Slaydren and exited from portal, when I walked back to Shura, my seeker of truth quest has a check mark, but it is not complete, and I can’t progress further in my main questline
Just figured out how to get past this. The description does not say this specifically but you have to do the dungeon on Hell 1 difficulty and not higher or it won’t work.
I also did it solo and not in a party. Not sure if that detail matters though.
You have to complete the dungeon solo without any assistance from a party of either celestial or real players. I had the same issue as mentioned above and was successful only when I played alone.